1. Field of the Invention
The present invention relates to an ink jet printing apparatus, an ink jet printing method, and a data generating apparatus by which a printing head capable of ejecting an ink and a processing liquid can scan a predetermined area of a printing medium a plurality of times to form an image by ejecting the ink onto the printing medium and to cover the formed image with the processing liquid.
2. Description of the Related Art
In recent years, ink jet printing apparatus has been widely used to provide printed images having higher definition, for public display applications and commercial display applications such as photographs, posters, and graphic prints. In the case of images formed for public display applications and commercial display applications, a requirement for high definition as well as a requirement for improving the image quality (e.g., uniform glossiness, bronze characteristic) and a requirement for improving the image toughness providing the strength and the long-term storage stability of the image. The bronze characteristic refers to a degree at which a color different from that of illumination light is reflected due to the bronze phenomenon when illumination light has mirror reflection (specular reflection) at an image surface. The bronze characteristic is known as being remarkable in a cyan ink in particular.
Ink coloring used in an ink jet printing apparatus is mainly classified as either a dye-base ink or a pigment-base ink. Dye ink includes coloring dye dissolved in water or alcohol medium in a molecular state and thus has a characteristic that dye ink is more transparent than pigment ink and provides superior color production. However, dye ink is disadvantageous in that early discoloring is caused due to ultraviolet light or an active gas in the atmosphere. On the other hand, pigment ink has a superior discoloring resistance in its long-term storage. In recent years, advanced manufacturing techniques have allowed pigment ink to establish both long-term storage stability (unique to pigment ink) and superior color production equal to that of dye ink. Thus, more ink jet printing apparatuses use pigment ink mainly for demanding commercial printing applications such as photographs and posters where a printed image must be stored for a long term.
However, an application using pigment as described above in particular still has the conventional image quality-related problems such as where the glossiness of images tends to be unequal and where the bronze phenomenon occurs as typical in pigment cyan ink. Another problem is that an increased number of display applications such as posters show a weaker image toughness and a poorer long-term storage stability compared to an offset-printed image, for example.
The following section will exemplarily describe the problem of abrasion resistance among the image toughness-related problems. The main problem is that an image printed on a glossy paper using pigment ink is easily damaged, even in general handling operation such as the subsequent handling and display.
FIG. 22A is a schematic view illustrating a cross section of an image formed by using a pigment ink on a printing medium having thereon an ink absorbing layer. The following section will described the reason why the image formed on a glossy paper by the pigment ink is easily damaged with reference to FIG. 22A.
A printing medium used for an ink jet printing apparatus is structured so that the surface of a base member (not shown) such as a paper or a film has thereon an ink absorbing layer 24 for the purpose of absorbing an ink. In order to reduce the oozing of the ink for example, the ink absorbing layer 24 includes a great amount of inorganic fine particles (of silica or alumina, for example) that are highly-absorptive to ink solvent. A printing medium used for the printing of a photograph such as glossy paper must have a flat and smooth surface, and thus generally uses inorganic particles having a dimension of the order of less than a micrometer. Thus, the gap between inorganic fine particles formed in the ink absorbing layer 24 is proportional to the particles diameter and thus is formed by fine pores having a dimension of the order of less than a micrometer.
On the other hand, coloring pigment particles having a dimension of about 100 nanometers are dispersed in pigment ink. This prevents the coloring pigment particles from entering the ink absorbing layer 24, when the coloring pigment particles have a diameter larger than that of the fine pores of the ink absorbing layer 24. In this case, the coloring pigment particles remain on the surface of the ink absorbing layer 24 as if they are blocked by a filter. In the case of a printing medium such as glossy paper, the coloring pigment particles generally have a diameter larger than that of the fine pores of the ink absorbing layer 24. Thus, a pigment ink layer 25 is formed on the surface of the ink absorbing layer 24.
Due to the pigment ink layer 25 formed on the surface of the ink absorbing layer 24 as described above, the image surface is easily damaged when an external force is applied to the pigment ink layer 25. In some cases, the pigment ink layer 25 (image) may be peeled due to an external force. For this reason, images formed using pigment ink have frequently been considered to have abrasion resistance-related problems.
Japanese Patent Laid-Open No. 2000-153677 discloses a laminate film method to protect an image formed by a pigment ink by covering the printed face of the image by a cover film. Japanese Patent Laid-Open No. 2005-81754 discloses a liquid laminate method to cover the printed face of the image using transparent resin liquid. Japanese Patent Laid-Open No. 2003-170650 discloses a post-processing method to mix thermoplastic resin particles in the ink absorbing layer of a printing medium for pigment ink to subsequently heat the printing medium to adhere a pigment ink layer to the ink absorbing layer.
In the case of the laminate film method, the abrasion resistance-related problem can be solved by covering the image surface with a resin film having a high film strength. However, the image surface covered by the film deteriorates the original texture of the printing medium such as paper. The laminate processing also increases cost, because another apparatus different from a printing apparatus is required.
The liquid laminate method can carry out, just after the printing of the image, the liquid laminate processing in the same printing apparatus. However, in order to obtain a sufficient effect on the abrasion resistance, a film thickness of a few microns must be formed. As in the laminate film method, the original texture of the printing medium therefore deteriorates. As disclosed in Japanese Patent Laid-Open No. 2005-81754, a further higher abrasion resistance is practically required when a thin film having a thickness equal to or lower than 1 micron is formed.
In the case of the post-processing method, the types of printing media for which an improved abrasion resistance can be expected are limited, and a heating processing step is required, causing the apparatus to have a larger size.
The problem of the abrasion resistance as described above can be very effectively solved by forming a transparent layer on the top layer of the pigment ink layer 25 on glossy paper to reduce the dynamic friction coefficient of the image surface. In recent years a configuration has been suggested for an ink jet printing apparatus to use a glossy paper including a transparent layer formed by a processing liquid including resin having an abrasion resistance function to print an image.
FIG. 22B is a schematic view illustrating a cross section of an image having a transparent layer formed on it by a processing liquid. A transparent layer 26 of the processing liquid is formed on the outermost surface so as to cover the pigment ink layer 25. The transparent layer 26 prevents the image surface of the pigment ink layer from being peeled or damaged by an external force (e.g., contact with a nail), thus providing the image with an improved abrasion resistance.
Japanese Patent Laid-Open No. H8-216432 discloses a general method to apply the processing liquid as described above. In the general method, in order to improve the water resistance of an image formed by an anionic dye ink, a processing liquid including cationic substance is applied after the application of the anionic dye ink. This method uses a multi-path printing apparatus to apply the ink to a printing medium through a plurality of scannings to print an image. At the final printing in the plurality of printing scannings (final printing scanning), the processing liquid is ejected to a position at which the ink was ejected, based on the ejection data for the processing liquid.
Covering the outermost surface of a printed ink image on a printing medium with a transparent layer is very effective to improve an image performance such as abrasion resistance. However, in order to apply the processing liquid to the entire surface of an image printed by pigment inks of a plurality of colors, a relatively large amount of processing liquid is required as compared to the amount of each color of the pigment ink. This has caused problems such as requiring a large size ink tank for the processing liquid and an increased running cost due to an increased consumption of the processing liquid, for example.
When the processing liquid is applied only in the final printing scan as disclosed in Japanese Patent Laid-Open No. H8-216432, the processing liquid is applied through a single scanning. This creates a case where the processing liquid may be applied in an amount exceeding the limited total amount of the liquid that can be absorbed by the printing medium at one time. In this case, the excessive liquid may cause problems in the image performance, such as a flooded ink phenomenon, bleeding, beading, defective drying, and a interference pattern phenomenon due to the transparent layer finished to have a mirror surface. When the multi-path printing apparatus is structured so that the processing liquid is ejected through ejection openings of a printing head only in the final printing scan, ejection openings for ejecting the processing liquid are concentrated within a specific area, thus causing a risk of a lack of durability of the printing head. When a printing head for ejecting ink is used as the printing head for ejecting the processing liquid, only a part of a plurality of ejection openings existing in the printing head for ejecting the processing liquid is used to eject the processing liquid and the other ejection openings are not used, wasting ejection openings.